1. Field of the Invention
This invention relates to a shield-type tunneling machine, wherein a degree of opening of slits provided in a cutter disc and a cutting angle of the bits with respect to the facing are freely adjusted.
2. Description of the Prior Art
In the so-called earth-pressure-resisting type, shield tunneling method as disclosed in Japanese Patent Public Disclosure No. 54-22933, a liquid such as sludge is caused to act on the facing ground under a pressure substantially equal to an underground water pressure in the facing, and a degree of opening of respective cutter slit is controlled, so that a cutter head can be pressed on the facing ground under a pressure larger than an active earth pressure of the facing ground but smaller than a passive earth pressure thereof, preventing the collapse of the facing.
In order to carry out such a method, a shield-type tunneling machine must be equipped with a mechanism for adjusting a degree of opening of slits in a cutter disc. A conventional slit-opening adjusting mechanism has been such that, for example, as disclosed in the aforesaid Public Disclosure, bits are slidingly moved from the slits towards or away from the facing, so that, according to a degree of movement of the cutter bits relative to the facing, the opening of respective slits may be adjusted.
Such a mechanism, however, has various drawbacks. One is that an angle of the cutter slits with respect to the ground, namely, a cutting angle, can not be adjusted, with the result of the limited application of the tunneling machine to a soft soil alone. Another drawback is that there is no countermeasure against gravels or the like jammed in gaps between the cutter bits and the slits. A further drawback is resulting in an incomplete sealing between the cutter bits and the slits and the complicated machining process.